Letterbox With Letter-Counting Facility

Description

Here is a simple Smart Letter-Counting Circuit that starts counting when you insert a letter in the letterbox at your home or office. It is designed to save your time from going to the letterbox to check if there are letters inside. The number of letters present in the box is indicated by a seven-segment display.

When a letter is inserted into the Letterbox With Letter-Counting, it passes between transmitter and receiver. This change in resistance provides a triggering pulse to pin 2 of IC1, generating a short-duration square-wave pulse at its output pin 3. This pulse acts as the clock input for the counter and displays driver CD4033 (IC2). Output pins of IC2 are connected to various segments a, b, c, d, e, f, and g pins of the seven-segment display (DIS1) as shown in the circuit.

This Letter-Counting Facility's common pin 3 is connected to the ground through current-limiting resistor R6. Alternatively, you can also provide a resistor each for each segment after removing resistor R6. Seven-segment display DIS1 displays the number of letters present in the box up to nine.